1. Technical Field
The present invention relates to an acoustic wave device and a method of manufacturing an acoustic wave device.
2. Related Art
An acoustic wave device that makes use of a propagation characteristic or a resonance characteristic of acoustic vibration of a surface acoustic wave (SAW) or a bulk acoustic wave (BAW) is known as an example of various devices such as a filter, an oscillator, a resonator and a convolver. Such an acoustic wave device includes a piezoelectric body and a pair of electrodes formed on the piezoelectric body for, when electrified, generating acoustic vibration in the piezoelectric body.
As an example of the acoustic wave device, there is known a device in which a silicon dioxide layer composed of silicon dioxide is formed to make contact with a piezoelectric body and/or electrodes for the purpose of temperature compensation, surface protection and so forth (see, e.g., JP-A-5-37284 and JP-A-6-164294).
For example, JP-A-5-37284 discloses an acoustic wave device in which a silicon dioxide layer, electrodes and a piezoelectric body are deposited one atop another on a hard layer formed of diamond or diamond-like layer. Furthermore, JP-A-6-164294 discloses an acoustic wave device in which a diamond-made hard layer, electrodes, a piezoelectric body layer and a silicon dioxide layer are deposited one atop another and an acoustic wave device in which a diamond-made hard layer, a piezoelectric body layer, electrodes and a silicon dioxide layer are deposited one atop another.
The silicon dioxide layer provided in such acoustic wave devices has an amorphous structure but it is known that the layer quality thereof varies largely with a manufacturing method, manufacturing conditions and the like (see, e.g., JP-A-2005-268798). As taught in JP-A-2005-268.798, examples of a typical method for forming the silicon dioxide layer include a sputtering method, a CVD method, a thermal oxidation method and a plasma oxidation method.
In the meantime, it is known that the characteristics of the acoustic wave devices noted above are affected by a constituent material of the devices. Particularly, in an acoustic wave device using a high frequency to deal with high-frequency signals, the constituent material thereof heavily affects the device characteristics.